1. SPOKE Cavities frequency preparation plan and RF control procedures
Cecilia G. Maiano

2. Technical Commissioning of Systems
After the handover from In-Kind Contributors and the testing at TS and tunnel installation the technical commissioning phase will start at ESS
Planning has started at ESS, in order to define a proper structure in the Linac group/SRF section and set necessary procedures for this activities
This presentation collects material for discussion, in order to properly match IK requirements and FREIA testing procedures to the information that will be needed during the technical commissioning activities
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3. Spoke Test/ Turn on Procedure Discussion - C.Maiano
Operation readiness
Before switching RF on, the ESS technical commissioning team will have to verify the ”operational readiness” of the modules, which is largely based on data collected by IK and TS activities
E.g. are the cavities in the expected state? Are all subsystems functional? Are all connections properly routed? Are all interlock thresholds set to safe values?
Operation Modes defined by ESS-34178
The technical commissioning team will need to handle the relevant interfaces with MPS and local technical interlock systems
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4. Reference data from IK and testing
First discussions during the RF Cell Review (May 2017) and with MPS and interlock experts pointed out the need to have, during the technical commissioning, a fast access to the handover state of all systems
Performance data of all tested cavities (in VT and at TS)
E.g. Q vs Eacc curves, limitation mechanisms during tests, reference frequencies in various conditions (warm, cold before tuner action), probe calibration coefficients, nominal transmissions, cable calibrations, etc.
Full understanding of the operation of all subsystems
E.g. expected steps to tune, nominal tuner response per step, warm and cold coupler conditioning procedures and experience, etc.
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5. 1. Need for a local database
At ESS we are settin up a system to handle the management of these data, in order to
Verify operational readiness
E.g. nothing unexpected has changed during storage and installation
Make properly informed decisions by the SRF section of all operational limitations and correspondingly set the interlock protection levels
E.g. Max field of a cavity before quench limitation or avoiding eccessive field emission regions, coupler conditioning signals, etc.
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6. Proposed path for the data
All IK partners store production and test data during their activities, e.g.
BW frequencies at warm/cold, transmissions, field flatness
Antenna Qext and calibrations, cable calibration
Power rise curves
Position of harmful HOM modes
We have to agree on a mechanism to transfer the data for consolidation at ESS, in a storage area accessible by the ICS, the commissioning/operation group and IKC.
consolidation is ESS responsibility, IK partner submit data in any suitable “standardized” form that can be used to feed it
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7. Data documentation/transfer
Example of an elliptical cavity
(using our XFEL 3.9 GHz data)
Passband measurement are retrieved from cavity producer and during the module assembly stage (any form used at IKC)
Normalization to ESS ICS standard (HDF5, Nexus extension) => ESS Task
Analysis logic built on the collected data (e.g. visualize, compare, etc.) => ESS Task
We can implement it also for spokes
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8. 2. Need for a “user manual”
Design criteria and test experience during the R&D and prototyping phase is documented by a large amount of reports, scientific and conference publications, by the IK contributors
It is often a ”work in progress” snapshot, on the path to the technical maturity of the series components, one should be careful to extract values
The ESS team/ SRF section needs to ”take ownership” of all design aspects and the valid design parameters
Compile a summary report in consultation of IK partners and reach consensus for its finalization
For “RF experts”, physics-oriented. Not just list of numbers, but design motivation
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9. Agreed path for the design information
I am compiling a “summary” of all the current information concerning the cavity design (spokes and elliptical) and nominal system and subsystem parameters, starting from published material from the IK and involving the IK for the completion, its review and its finalization
Focus is on the understanding of all design background in order to fulfill the goals of the technical commissioning phase at ESS
Develop procedures at ESS for verification and measurement activities
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10. Example from the SPK document
(+…)
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SPK document (2)
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SPK document (3)
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13. Example: Frequency preparation
What are the expected cavity frequencies during all stages?
Uncertainties?
At least for the technical commissioning we will foresee measurements before proceeding to the further OM
Goal frequency at 2 K
(before CTS)?
Assuming cavity sens tolerance
kHz/mm
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14. Typical questions (SPK example)
Hard limit of tuner range to be enforced?
N. Gandolfo < 1.18 mm (~170 kHz)
to limit stress < 400 Mpa
Then goal frequency at cold need to be higher (including its estimated spread, which should then be quantified)
Minimum value for the CTS action
e.g. for piezo preload: kN
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MBL/HBL Example
Requirements exists but are not readily usable for checks in OM1 (Ready for cooldown) or OM5 (Stand-By at 2 K). Commissioning team needs full strategy
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Summary
Requirements and Interface specifications are extremely important for the success of the project, but are not sufficient
Technical commissioning of all systems will require the full understanding by the ESS team/SRF section of all design details
These are not necessarily captured by requirement / interface specifications
“Knowledge transfer” from the IKC to the project team!
“Data transfer” to enable assessments and decisions by the project team from the IKC experience
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